It is well known to supervise proper function of an alternator and associated rectifier equipment as well as of an associated voltage regulator in various types of networks; when installed in an automotive vehicle--to which reference will be made in the present application--it is usually customary to provide a charge control instrument, typically a charge control lamp, which is connected to the positive supply bus of the on-board network, to which also the positive terminal of the battery is connected, and further to a junction which is formed by the voltage regulator input. This junction is usually also connected to exciter diodes which form part of the d-c output of the alternator. The charge control lamp will light if the voltage difference between the positive bus and the other terminal of the lamp exceeds a predetermined level. If the prime mover driving the alternator--typically an automotive engine--is stopped, and the main switch, for example the ignition switch, is closed, the positive terminal of the battery is connected to one terminal of the charge control lamp. Current flow will then occur from the positive main bus of the vehicle to ground or chassis. The charge control lamp can be replaced by a moving pointer indicator of the volt meter type.
It is also known to connect an ammeter between the positive terminal of the battery and the positive bus of the vehicle. Usually, the starter terminal is bypassed. If the alternator or generator output is insufficient, or the alternator is defective, or the voltage regulator is defective, the current flowing through the ammeter will be excessive, thus providing a malfunction indication to the operator.
The charge control lamp cannot determine defects which can arise within the voltage regulator itself, for example short circuit of the main power transistor thereof which would cause substantial rise in the voltage of the network, resulting in damage to the battery. The charge control lamp itself, for lighting, requires certain voltage differences and current supply thereto adequate to cause the filament to light. Low output of the alternator, for example due to malfunction of the rectifier diodes, can hardly be recognized by the charge control lamp.